Chapter 11 Reorganization (Schedule Of Chapter 11 Reorganization Cash Flows) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Cash flows from operating activities:
Net loss	$ (396,230)	$ (255,721)	$ (858,115)
Adjustments to reconcile net loss to net cash provided by operating activities:
Depreciation, depletion, amortization and accretion	146,793	271,410	400,848
Deferred income taxes	2,041	3,247	(61,058)
Reduction in value of assets	26,897	17,186	322,714
Reduction in value of assets held for sale	114,213	76,577	417,011
Right-of-use assets amortization	20,224	20,613
Stock-based compensation expense	2,628	19,814	31,451
Bad debt	12,473	76	(16,957)
Reorganization items	18,087
Other reconciling items, net	(8,309)	(16,023)	(9,545)
Changes in operating assets and liabilities:
Accounts receivable	111,948	104,462	(33,159)
Inventory and other current assets	27,933	(6,137)	(7,559)
Accounts payable	(35,170)	(12,278)	8,912
Accrued expenses	(18,154)	(37,482)	(21,113)
Other, net	(23,157)	(39,316)	(8,373)
Net cash provided by operating activities	2,217	146,428	165,057
Cash flows from investing activities:
Payments for capital expenditures	(47,653)	(140,465)	(221,370)
Proceeds from sales of assets	50,039	110,008	33,299
Net cash provided by (used in) investing activities	2,386	(30,457)	(188,071)
Cash flows from financing activities:
Delayed draw term loan commitment fee	(12,000)
Debtor in possession credit facility costs	(1,554)
Other	(432)	675	2,613
Net cash used in financing activities	(14,194)	(5,292)	(2,586)
Net change in cash, cash equivalents, and restricted cash	(7,204)	111,640	(28,735)
Cash, cash equivalents, and restricted cash at beginning of period	275,388	163,748	192,483
Cash, cash equivalents, and restricted cash at end of period	268,184	275,388	$ 163,748
Reorganization, Chapter 11, Plan Effect Adjustment [Member]
Cash flows from operating activities:
Net loss	(377,246)
Adjustments to reconcile net loss to net cash provided by operating activities:
Depreciation, depletion, amortization and accretion	112,395
Deferred income taxes	8,569
Reduction in value of assets	21,049
Reduction in value of assets held for sale	114,213
Right-of-use assets amortization	16,107
Stock-based compensation expense	2,344
Bad debt	12,377
Reorganization items	18,087
Other reconciling items, net	(4,569)
Changes in operating assets and liabilities:
Accounts receivable	96,851
Inventory and other current assets	27,856
Accounts payable	(19,282)
Accrued expenses	(18,089)
Income taxes	(12,208)
Other, net	(3,509)
Net cash provided by operating activities	(5,055)
Cash flows from investing activities:
Payments for capital expenditures	(41,179)
Proceeds from sales of assets	49,792
Net cash provided by (used in) investing activities	8,613
Cash flows from financing activities:
Delayed draw term loan commitment fee	(12,000)
Debtor in possession credit facility costs	(1,554)
Other	(640)
Net cash used in financing activities	(14,194)
Net change in cash, cash equivalents, and restricted cash	(10,636)
Cash, cash equivalents, and restricted cash at beginning of period	223,702
Cash, cash equivalents, and restricted cash at end of period	$ 213,066	$ 223,702